Nickel base alloy for service at high temperatures



United States Patent 3,005,704 NICKEL BASE ALLOY FOR SERVICE AT HIGH TEMPERATURES William H. Faulkner, Kokomo, Ind., assignor to Union Carbide Corporation, a corporation of New York No Drawing. Filed July 23, 1958, Ser. No. 750,316 3 Claims. (Cl. 75171) This invention relates to a nickel-base alloy tor use at high temperatures and, more particularly, to alloys suitable for use in applications where superior stress-rupture characteristics at high temperatures are required.

High temperature alloys capable of withstanding increased stresses and having a longer useful life are in increasing demand. Due to research developments in recent years, many commercial alloys perform exceptionally well at much higher temperatures than those produced only a decade ago. Present day improvements are made in smaller increments; for example, an increase of only 25 to 50 F. in the useful temperature range of an alloy is presently considered a major contribution by users and producers of the type of alloy in question. Some high-temperature alloys have excellent oxidation resistance, others have exceptional thermal shock resistance, or very good creep and stress-rupture properties. Generally speaking, each alloy has one or two specific characteristics which are outstanding, but falls short in other respects. This situation, though unfavorable, is recognized by most fabricators, who accept this limitation in their operations. For example, certain nickel-base alloys possess the desired degree of stress-rupture and tensile strength but fall short in impact and/ or ductility properties. Other alloys of a similar type, though possessing an acceptable range of impact strength and ductility, lack sufiicient stress-rupture and tensile strength to meet the requirements of fabricators and users in the high temperature nickel-base alloy field.

For example, specific reference may be made to an alloy containing about 5 to 20 percent chromium, about '5 to 15 percent molybdenum and about 4.5 to 6 percent aluminum with the remainder substantially all nickel. This alloy displays strength to endure a stress of about 50,000 psi. for 100 hours at 1500 F; 27,300 psi for 1000 hours at 1500" F.; 9,500 psi. for 100 hours at 1800 F.; and nearly 5,000 psi for 1000 hours at 1800 F.; however, the ductility and impact properties of this alloy at temperatures ranging up to 1900 F. fall short of the minimum requirements for certain applications, as for instance, gas turbine parts. Another nickel-base alloy containing about 18 to 22 percent chromium, 8 to 10 percent molybdenum, 2 to 3 percent titanium, 0.5 to 2 percent aluminum, and the balance essentially nickel, has good thermal shock resistance and adequate strength for some applications, but is completely unacceptable at temperature levels ranging up to 1900 F. if ductility and impact strength are also required.

The primary object of the invention, therefore, is to provide an alloy which has higher tensile, stress-rupture, and creep-rupture strengths than those alloys currently used, together with sufiicient ductility and impact proper- "ice parent from the following description and appended claims.

In accordance with the present invention, a nickel-base alloy is provided consisting essentially by weight of between 10 and 20 percent chromium, between 4 and 7 percent molybdenum, between 6 and 8.5 percent aluminum, between 0.01 and 0.15 percent boron, between 0.01 and 0.50 percent zirconium, and the balance substantially all nickel. Manganese and silicon may each be present in the alloy up to 1.00 percent; carbon and iron may be present in amounts up to 0.05 percent and 5.0 percent respectively; and the impurities'phosphorous and sulphur may be present in amounts up to 0.030 percent and 0.015 percent, respectively.

The preferred range of essential constituents of this alloy consistss essentially by weight of between 14 and 16 percent chromium, between 4.25 and 5.75 percent molybdenum, between 6.40 and 7.10 percent aluminum, between 0.05 and 0.12 percent boron, between 0.01 and 0.20 percent zirconium, and the balance substantially all nickel.

The preferred composition of the alloy is 15 percent chromium, 5 percent molybdenum, 6.7 percent aluminum,

ties to enable its use in a wide variety of applications at temperatures higher than the current operation temperatures, and up to a temperature of about 1900 F.

Another object of this invention is to provide an alloy with high oxidation resistance at elevated temperatures.

A further object of this invention is to provide an alloy for use under severe service applications which may be produced at a relatively low cost, the constituents of which are not strategic metals and are readily available as raw materials.

Other aims and advantages of the invention will be ap- 0.07 percent boron, 0.10 percent zirconium, the balance being essentially nickel.

The proper control of zirconium, it has been discovered, improves both the ductility and the strength at high temperatures and also minimizes variations of these properties in either the cast or wrought form. At the zero or very low zirconium level, the alloy is relatively brittle; at the higher zirconium level, however, the alloy becomes more ductile and can be forged. Accordingly, zirconium in the range prescribed is an essential constituent of the alloy of this invention.

Chromium content must be controlled within the 10 to 20 percent range, and is preferably held at 15 percent to complement aluminum in imparting oxidation resistance. Chromium contents higher than 20 percent would reduce the amount of nickel available for the formation of nickel-aluminum intermetallic compounds upon which high-temperature strength mainly depends.

Molybdenum is added as a strengthening element but should be controlled between 4 and 7 percent and preferably about 5 percent, because molybdenum contents above these limits will reduce oxidation resistance and ductility to an undesirable degree. Molybdenum also increases density and increases the costs.

Iron may be tolerated as an impurity; however, it should not be present in the alloy in an amount more than 5 percent because it does not contribute to strength. Above 5 percent, iron acts as a diluent and reduces the availability of nickel for intermetallic compound formation.

It has been found that carbon should not be present in excess of 0.5 percent because it increases room-temperature brittleness and does not improve high-temperature strength.

Boron above 0.15 percent reduces room-temperature ductility. It has been found that about 0.07 percent is the preferred boron content.

Aluminum strengthens nickel-base alloys through the formation of an intermetallic compound, Ni Al, which is contents of aluminum in nickel-base alloys produce many metallurgicai advantages, among them can be cited increased strength, increased oxidation resistance, lower costs and lower density.

In the investigation leading to the invention of this alloy for long time service between l700 and 1900'F. and under high loads, it was learned that some elements usually found in nickel-base alloys, such as titanium, columbium and tantalum, not only do not benefit the alloys, but in some cases, actually reduce the strength characteristics at elevated temperatures or otherwise adversely aifect the alloy.

Therefore, titanium content should be kept as low as possible, because this element increases the solid solubility of aluminum in the matrix and thereby reduces the amount of Ni Al precipitate. The reduction of Ni Al precipitation content weakens the alloy as shown by the results of a series of tests on an alloy of the following composition: 15 percent chromium, 5 percent molybdenum, 6.6 percent aluminum, 0.13 percent boron, 0.1 percent zirconium, 5 percent iron, the balance nickel plus varying amounts of titanium.

' STRESS-RUPTURE DATA [Tested at 1700 F. and 22,000 p.s.i.]

Titanium, percent: Life, hours 0 127.5 0.38 19.4 0.39 30.6 0.88 46.9

ROOMTEN[PERATURE TENSILE TEST DATA Ultimate Yield 7 Reduction Oolumbiurn, Strength, Strength Elongation, of Area, Percent p.s.i. at 0.2% Percent Percent p.s.i.

0 132, can 111,000 6 13 2 130, 000 120, 000 3 7 STRESS-RUPTURE DATA [Tested at 1700 F. and 22,000 psi] R eduction Columbiurn, Percent Life, Elongation, of Area, Hours Percent Percent Although columbium may slightly increase the stressrupture strength, the attendant ductility has been reduced to-a point where the alloy is practically useless in severe service applications in the temperature range of from 1500 F. to 1900 F. Without columbiurn, the alloy has sufiicient ductility and malleability to be forged at tem- .peratures of about 2050 F.

The improved nickel-base alloy of the invention may be melted by any furnacing procedure, as for instance, by are or induction-melting pratcice. Melting may be conducted in normal atmosphere but additional benefits may be derived by melting in a vacuum or in the protective atmosphere of an inert gas. Heat-treatments enhance the properties of the alloy but are not essential for general application of the alloy, which may be used in the 'as -cast condition. p

The following average properties were determined for forged specimens of the preferred alloy composition after heat treatment for 30 minutes at 2075 F. and air-cooled.

Wrought product properties ROOM-TEMPERATURE TENSILE DATA Ultimate Yield Elongation Reduction Strength Strength, One of Area, psi. 0.2% Oti- Percent set p.s.i. Percent STRESS -RUPTURE DATA AT 1800 F. WITH 16,000 P.S.I. STRESS Elongation Reduction Life, Hours In One Inch, of Area, Percent Percent 7 AVERAGE STRESS RUPTURE DATA 1,500 F. l,800 F.

Hour 1,000 Hour 100 Hour 1,000 Hour Lite, Psi. Life, psi. life, p.s.i. Life, psi.

The average tensile test data for this alloy, when heattreated for 30 minutes at 2100 F. and subsequently aircooled, are as follows:

TENSILE TEST RESULTS Ultimate Yield Elongation Reduction Test Strength, Strength at In One of Area, Temperature, F. p.s.i. 0.2% Ofi- Inch, Percent set p.s.i. Percent Charpy V-notch impact data for the instant'alloy were also determined in the heat-treated condition (30 minutes at 2100 F; and air cooled). The following results are the average of several tests and substantiate the high degree to which the alloy resists impact at room and elevated temperature.

Test temperature, F. Impact resistance, ft.-lb. Room 10.3 1200 8.6 1500 V 9.3 1700--- 12.0 1900 15.0

rupture strength at elevated temperatures, said alloy consisting essentially by weight of 14 to 16 percent chromium, 4.25 to 5.75 percent molybdenum, 6.40 to 710 percent aluminum, 0.05 to 0.12 percent boron, 0.01 to 0.20 percent zirconium, up to about 0.05 percent carbon, and the balance substantially all nickel.

3. A nickel-base alloy characterized by high stress-rupture strength at elevated temperatures, said alloy consist ing essentially by weight of about 15 percent chromium,

about 5 percent bolybdenum, about 6.7 percent aluminum, 10

about 0.07 percent boron, about 0.10 percent zirconium, up to about 0.01 percent carbon and the balance being substantially all nickel.

References Cited in the file of this patent UNITED STATES PATENTS 2,575,915 Guy Nov. 20, 1951 2,621,122 Gresham et al Dec. 9, 1952 2,912,323 Bieber et al. Nov. 10, 1959 2,920,956 Nisbet et a1. Jan. 12, 1960 FOREIGN PATENTS 133,745 Australia Aug. 3, 1949 OTHER REFERENCES National Advisory Committee for Aeronautics Technical Note 4049; Decker et al., June 1957, 34 pp. 

1. A NICKEL-BASE ALLOY CHARACTERIZED BY HIGH STRESSRUPTURE STRENGTH AT ELEVATED TEMPERATURES, SAID ALLOY CONSISTING ESSENTIALLY BY WEIGHT OF 14 TO 16 PERCENT CHROMIUM, 4.25 TO 5.75 PERCENT MOLYBDENUM, FROM 6.40 TO 7.30 PERCENT ALUMINUM, FROM 0.05 TO 0.15 PERCENT BORON, FROM 0.01 TO 0.50 PERCENT ZIRCONIUM, UP TO ABOUT 0.05 PERCENT CARBON, AND THE BALANCE SUBSTANTIALLY ALL NICKEL. 